This invention relates to multi-phase polymer blends of vinylidene fluoride (VDF) based polymers, especially to such blends wherein at least one of the polymers is a VDF-based copolymer and wherein the properties of the polymer blends can be tailored to meet the intended application. xe2x80x9cCopolymerxe2x80x9d is used herein in its broadest sense to include polymers made from at least two different monomers, such as terpolymers. The blends are useful in a variety of applications, such as wire and cable, pipe and liner applications, sheet extrusion, polymer foams, thermoforming, injection molding and rotational molding.
While many commercially available polyvinylidene fluoride (PVDF) homopolymers and VDF-based copolymers, such as VDF/hexafluoropropylene (HFP) and VDF/chlorotetrafluoroethylene (CTFE) copolymers, already have properties (such as good tensile strength, flexibility and the like) that make them suitable for certain applications, it would be useful to have a method of combining such polymers so as to be able to enhance certain properties, such as resistance to chemicals and impact resistance, for specific end-use applications.
Blends of PVDF homopolymer and VDF-based copolymers have been disclosed in U.S. Pat. No. 5,429,849, but they only cover single phase blends with 25-75 weight % PVDF. VDF-based copolymers useful in this invention have been disclosed, for example, in U.S. Pat. No. 6,187,885 on VDF/HFP copolymers and in U.S. Pat. No. 4,946,900 on VDF/CTFE copolymers. For the purpose of this application, the copolymers described in these latter two patents will be herein referred to as xe2x80x9cheterogeneousxe2x80x9d copolymers.
Multi-phase polymer blends are provided which comprise a VDF-based copolymer and at least one other polymer selected from PVDF homopolymer or another VDF-based copolymer, as well as various applications of such polymer blends for wire and cable, sheet, injection molding, rotomolding, pipe and tube, and the like. Preferred copolymers are the VDF/HFP and VDF/CTFE copolymers, particularly the heterogeneous VDF/HFP and VDF/CTFE copolymers described in the foregoing paragraph.
It has now been found that two or more different VDF-based polymers can be mixed to create multi-phase blends which match certain properties of existing copolymers while enhancing certain other properties so to custom make polymers suitable for specific end uses. These blends are made by using methods known in the art to create homogeneous dispersions of VDF-based polymers, such as by melt mixing via extrusion. Other methods include latex blending, powder blending, solvent blending and the like.
While the detailed discussion below will focus on the VDF/HFP copolymers, this invention is also applicable to VDF-based copolymers made by substitution of one or more other comonomers, such as CTFE, tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (PMVE), perfluoroalkyl vinyl ether (PAVE), vinyl fluoride (VF) and/or trifluoroethylene (TFE), for some or all of the hexafluoropropylene.
For example, as shown below, it is possible to substantially duplicate many of the properties of a VDF/HFP copolymer containing 10 weight % HFP, while enhancing its impact resistance and chemical resistance, by creating either (a) a 43/57 weight blend of a PVDF homopolymer with a VDF/HFP copolymer having about 17 weight % HFP wherein the blended polymers have essentially the same viscosity or (b) a 50/50 weight blend of a VDF/HFP copolymer containing about 5 weight % HFP with a VDF/HFP copolymer containing about 15 weight % HFP wherein the blended polymers have essentially the same viscosity.
In the examples below, the polymers and blends were extruded with a twin screw extruder and the test specimens required for mechanical testing were produced by injection molding. Mechanical testing, such as Izod impact resistance, chemical resistance testing and the like are then performed on the polymers.